The invention concerns a part checking fixture and, in particular, a fixture for verifying the configuration of a curved hollow tube.
Many tubular parts are formed as a series of curved and straight portions to achieve a desired configuration. Of course, each curved and straight portion has a set of tolerances associated with it. Therefore, some method of checking the configuration must be used in order to determine that the ends of the tube can be connected where desired and the tube will follow a path between the ends which will not interfere with anything positioned therealong. The acceptable path is known as an "error envelope".
Although well known, the "error envelope" is difficult to check since each set of tolerances for a portion is dependent upon all of the other sets of tolerances for the part in order to determine an acceptable position for the part in space. One known method of checking tolerances is to utilize blocks to locate the straights of a tube or a hose. A second known method utilizes a rigid fixture with saddle gages that indicate the deviations of the tube straights from the nominal dimensions. Another known method of checking a part is to build the "error envelope" into a fixture into which the parts are inserted. The ends of the tubular parts are located utilizing pins inserted through an aperture in a block on the fixture and engaging an open end of the tubular part. However, such pins commonly are lost thereby rendering the fixture unfit for use until a replacement pin is provided.